Apparatus for producing a master dot pattern for photo-etching of a graded hole shadow mask

ABSTRACT

Apparatus for the production of master dot patterns for photoetching a graded-hole shadow mask for use in a color picture tube comprising mounting a grading mask having its transparency concentrically, progressively decreasing from the center toward the periphery thereof between a light source and a photographic material and inserting a screen between the grading mask and the light source.

United States Patent 1 [1 1 Noguchi APPARATUS FOR PRODUCING A MASTER DOTPATTERN FOR PHOTO-KITCHENS OF A GRADED HOLE SHADOW MASK [75] Inventor:

Kinichi Noguchi, Tokyo, Japan Assignee: Toppan Printing Co. Ltd., Tokyo,

Japan Filed: July 2, 1971 Appl. No.: 159,335

Related U.S. Application Data Continuation of Ser. No. 883,668, Dec. 22,1969, which is a continuation of Ser. No. 387,724, Aug. 5, 1964,abandoned.

[52] US. Cl 95/1 R [51] Int. Cl. G03b 27/16 [58] Field of Search 95/1;355/84 [56] References Cited UNITED STATES PATENTS 1,953,471 ,4/1934Eich 96/27 Oct. 30, 1973 3,385,184 5/1968 Ramberg 95/1 2,717,545 9/1955Engeler 355/84 3,109,117 10/1963 Kaplan 95/1 X Primary Examiner l0hn M.Horan Att0rney-Eric l-l. Waters et al.

[57] ABSTRACT Apparatus for the production of master dot patterns forphoto-etching a graded-hole shadow mask for use in a color picture tubecomprising mounting a grading mask having its transparencyconcentrically, progressively decreasing from the center toward theperiphery thereof between a light source and a photographic material andinserting a screen between the grading mask and the light source.

9 Claims, 12 Drawing Figures PATENTEDucI 30 I973 SHEET 10F 3 FIG? F/GJ

PAIENIEDncwso ms M a; 768L385 SHEET 2 UF 3 FIG. 6

8 G H 0 T m 5 mwhmiio ,3 Ba

FIG. 7

DISTANCE FROM DISC CENTER PAIENTEDnmoms 3.768385 SHEET 3 UF 3 R Dm \7 Ira U C) E 3 6 Q q 0 Dm 0 r DENSITY OF GRADING MASK DISTANCE FROM DISCCENTER F G. .9 Fl 6. /0

t g LLI Q 0 EXPOSE VALUE L065 APPARATUS FOR PRODUCING MASTER DOT PATTERNFOR PHOTO-ETCHING OF A GRADED HOLE SHADOW MASK CROSS-RELATED APPLICATIONThis is a Continuation Application of Application Ser. No. 883,668 filedDec. 22, 1969 (issuedias U.S. Pat. No. 3,745,734 on- Feb. 29', 1972).which in turn is a Streamlined Continuation of Application Ser. No.387,724 filed Aug. 5,1964 and now'abandoned.

' BRIEF SUMMARY or THE INVENTION This invention relates to apparatuszformanufacturing a master dot pattern for photo-etching a graded-holeshadow mask used in'a color television picture tube and has particularreference to a grading mask used therein.

Existing shadow masksused' for color picture tube are, in most cases,made of aethinisheet of steel-orother metal which is provided with a.number of regularly aligned pores to permit the transmission of: anelectron. beam therethrough. More recentimprovements in this type. ofshadow mask comprise the provision of relatively large poresin thecenter-of the effective mask area and reduction of the size ofconcentrically aligned pores progressively toward the peripheral portionof the mask while eliminating amiss landing of electrons at theperiphery of the screen of the tube. This. is termed a graded-holeshadow mask" whichis manufactured by a photo-etching process.-

Itis aprincipal objectof this invention to provide apparatus forpreparing amaster dot'pattern'for photoetching of graded hole shadowmaskswhich is provided with'a dot diameter larger at-the center of theeffective surface and progressively smaller toward the peripheralportion of the mask.

It isanother object ofthe invention to provide apparatus 'formaking a;photo-etching master dot pattern with the use: of a-gradingmask adaptedto'control the intensity of exposure light so that the brightness of apicture is greater at the center and smaller toward the periphery of themask.

It is afurtherobject of theinvention to provide a photo-etching masterdot riatternwwhi'chhas a suitable pore size distribution by varying thedensityv of the grad ing mask. I

It is still another object of the invention to .provide simple,economical means for obtaining the above grading mask'for use inthe'manufacture of photoetching masterdot patterns.

These and other objects of theinventionwill become more apparent fromthefollowingdescription taken in connection with the accompanyingdrawings illustrativeof the-manner of preparingamaster dot pattern'forphoto-etching of graded-hole shadowzmasks according to the invention.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is aperspective view ofagradingmask according to the present invention;

FIG. 2'is aperspective .view of-a grading. mask using an optical wedgeaccording to thepresent invention;

FIG. 3' Ba perspective-view'of a gradingrnask using a plurality'ofsheets accordingtothe present invention;

FIG. 4 is aperspective viewot' a gradingmask in the form of a platewitha conical.- recess thereinaccording; to the present invention;

FIG. 5 is a front view of a glass screen for photographing a shadow masketching master dot pattern which has an angle of 60 cross-over of linegroups;

FIG. 6 schematically illustrates the arrangement of a device forphotographing a graded-hole shadow mask master pattern using a processcamera;

FIG. 7 schematically illustrates the arrangement of a device forphotographing a graded-hole shadow mask master pattern using a printingframe;

FIG. 8 is agraph illustrating the relation between the distance from thecenter of the effective area of the master dot pattern for photo-etchingof graded-hole shadow masks to the periphery thereof and the dotdiameter; I

FIG. 9 is a graph illustrating the relation between the grading maskdensity and the screen dot diameter where the photographic material,time of exposure and development conditions are all fixed for thescreening of the gradingmask placed in front of a light source in theproduction of a shadow mask pattern;

FIG. 10 graphically illustrates the density distribution of the gradingmask obtained from the graph of FIG. 9;

FIG. 11 graphically illustrates the characteristic curve of a dry'plateused in the manufacture of a grading mask; and

FIG-412 graphically illustrates an opening in a disc hereinafterreferred-to as sector-disc which is used in the'manufacture of a gradingmask.

DETAILED DESCRIPTION Generally, a master dot pattern required forphotoetching of shadow masks may be obtained by passing thereto a lightbeam passed through a screen having a transparent spot at each comer ofan'equilateral triangle. In such'instance, the pattern may be subjectedto screening through a lithographic glass screen or contact screen 3.having a rhombic opening 2 with an angle of 60 for crossing of linegroups 1, as illustrated in'FIG. 5,- thereby obtaining dots of uniformsize over the entire surface of thepattern.

border to vary the dot size successively from the effective center areatoward the periphery of the pattern, the present invention contemplatesthe use of a grading maskwhich may be placed in front of a light sourceto control the intensity of light therefrom.

The grading mask is based on an entirely new concept of the inventionand comprises a suitable photographic material such as dryplate, film orthe like which has alight transmittance which is high at the center andprogressively lower toward the peripheral portionof the mask, suchtransmittance variation being determined. by the distribution of thepore size required for the performance of a desired shadow mask;

As a result of extensivesearch for the best mode of producing theafore-mentioned gradingmask, the present inventor has discovered thefollowing:

l. Adisc member 11 having a transparent portion 11a and an opaqueportion11b; which is similar to a sector-disc as used' in a sensitom'eter, suchas for-example a I-Iurter-Driffield sensitometer anda Schinersensitometer, is held in opposingrelation to arelatively lowlighttransmittance.

the characteristic curve obtained from the tests conducted under thesame conditions as .in the manufac-- ture of the grading mask. Thisprocess has the advan-- tagethat a density. distribution isobtained withaccuracy as'desired, although the rotating center may be somewhatunstable.

2. As shown in FIG. 2,'an opaque disc 13 is provided with a transparentportion 13a having a suitable central angle and with an optical wedge13b having a predete'r-' mined density distribution superimposeduponsaid transparent portion. The opaque disc 13 is positionedinopposing relation to a relatively low contrast photographic material14. Light is passed through the disc member 13 to the photographicmaterial member 14 while either of the two members is rotated about anaxis coincident with the maximum density spot 15 of the optical wedge13b; Density distribution of the opti-' cal wedge 13b may be determinedby the characteristic curve'obtained from tests carried out underexactly the same conditions as provided forthe production of a gradingmask. This process has the advantage that the central angle is easilyfabricated and the'center of rota-. tion is established .with areasonable degree of accuracy. r v

As illustrated in FIG. 3, there are provided aplurality'ofsemitransparent sheets 16, 16, 16" 1 16 made of a synthetic resin filmor paper having a uniform transmittance of light. They are provided withcircular windows '17, 17, 17" 17, which are concentrically arranged butdifferent in diameter, and are stacked together with the sheet 16 havingthe smallest 4. The arrangement illustrated in FIG. 4 involves asemitransparent block 18 of a synthetic'r'esin or the like which hasuniform transmittance of light. The block is prevented with a conicalrecess andjis thinnest at the center 1 8a and becomes progressivelythicker toward vthe periphery of the recess. Alternatively, such patternmay be printed on a'photographic material. According to this process, agood selection of transparent materials may be of matte form on thesurface to act as a lens,

thereby allowing the gradingto vary as desired.

I follows.

A detailed description follows for the production of I the above gradingmasks according to the invention.

Process (1) Example v a. Determining the density distributionofthe-grading mask. 1

, Density distribution of the grading mask required for the preparationof a graded-hole shadow mask pattern having a requisite screen dot sizedistribution may be obtained in the following manner. I I

In the phtographing of a shadow mask pattern, the grading mask is placedin front of a light source and screened where the'photographic material,time of exposure and development conditions are held invariable.

In this manner, there may be established a certain relation between thegrading mask density and the screen dot diameter. This maybegraphicallyillustrated as A dry plate is placed on a turn-tableimmediately un derneath an enlarging lens in a manner similar to thefabrication-0f a grading mask. ,To the dry-plate is adhered a step wedgewhose density is known. It is exposed to .light for a suitable length oftime and then subjected to development under certain conditions. Bydetermining the density of the resulting dry-plate in view of the knowndensity of the step wedge, it is possible to obtain acharacteristiccurbe prevailing under such development conditions/SeeFIG. 11, from the exposure light intensity E required to obtain adesired density D maybe readily determined.

c. Determining the shape of the opening or transparent portion 11a inthe sector-disc.

(See FIG. 12). v

From the definition of exposure light intensity, there maybe establishedthe equation E=I-T where I is light intensityand T is exposure time. Iflight transmittance is uniform over the entire area of the transparentportion or opening in the sector-disc, the factor I remains constant,hence EaT. When light is applied while either of the sector-disc and thedry-plate is being rotated, the time of exposure Tr at point 7 away fromthe center of the disc is proportional to an arc length [r of the radiusof the opening in the sector-disc. The arc length l r is furtherproportional to the angle Or from the center of the disc, so that, theremay be established a relation defined by EaQ; that is, E=K-Q where K isan optional multiplier.

Accordingly, the sequenceof fabricating a grading mask may be given asfollowsm Y 1. The .value r is selected as often as required successivelyfrom the point 0.

2. The value D corresponding to each of the values is obtained from FIG.'10.

3.. T he value log E corresponding to each of the D values is obtainedfrom FIG. 11.

4. The value E is derived from log E thereby obtaining Q from theequation of E=K'Q. In this inu n r stance, the value K determines thetotal .size of a With reference to a curve drawn by connecting theplotted dots, a base having a transparent portion and an opaqueportionmay be prepared and subjected to photographing with a dry-platethereby'producing a sectordisc. This disc is carried in a negativeholder on an enlarger. A turn-table having a dry-plate holder mountedthereon and driven by a motor is placed immediately below the enlargerlens. With the image of the sectordisc projected onto the dry-plate, thecenter of the disc may be registered with the center of rotation of theturn-table.

i As a light source for theenlarger, there may be used a 100V, 150Wenlarger light bulb. The lens may have a focal length of 135mm and adiaphragm opening of f 22. While the turntable is rotated at a speed of78 rpm, a duplicating Olso dry-plate is exposed to light for 20 seconds.The dry-plate is developed with a specified developer to a low contrast.

Next. the manner in which photographing is made of a master dot patternfor photo-etching a graded-hole shadow mask according to the inventionwill be described in some detail as follows.

I. Photographing with process camera.

A. Equipment and material.

1. Camera.

A conventional camera with adjustable aperture is suitable for thepurpose.

2. Light source.

A highly stable light source such as a 100V, 500W tungsten projectionlamp used for an ordinary camera may besuccessfully used. A housing forthe lamp may incorporate a cooling fan, a heat absorbing filter and alight diffusing plate (opal glass). In front of this diffusing plate,there is installed a photographically or mechanically fabricated gradingmask having a brightness greater at the center and progressivelydiminishing away from the center of the mask.

3. Lens.

An ordinary lens (such as for example Aponicol F60cm) may be used with acontrolled round aperture or an iris diaphragm.

4. Screen. 7

A 60 cross angle glass screen provided with a rhornbic opening andhaving a width ratio of transparent portion to opaque portion of 1:1 1:2is suitable. Alternatively, a white dot screen having a circular orregular polygonal transparent dotat each comer of a equilateral trianglemay be fabricated from a dry-plate or film. The screen is secured to ascreen holder.

5. Photographic material.

This may be a dimensionally stable base lith type film or dry-plate. I

B. Process of preparing a pattern.

The apparatus required for the production of a master dot patterncomprises a light source 9, a heat absorbing filter 20 and a lightdiffusing plate 21 which are journalled in a-lamp housing (not shown)with a grading mask 22 placed in front of the diffusing plate 21, asshown in FIG. 6. Designated at 23 is a camera which is mounted beforethe grading mask.

Designated at 24 is the camera lens and at 25 is an iris diaphragm. Ascreen mounted in a screen holder is placed in front of the camera.

Designated at 26 is a photographic material'(dryplate or film).

An example of the above equipment, the camera lens is located about 300centimeters from a ground glass 24' the camera lens 24 having a focaldistance of 60 centimeters and mounted to 70 centimeters from the lightsource 9 and the diffusing plate 21. The diffusing plate 21 has mountedthereon the grading mask 22 with a diameter of about 10 centimeters, theperiphery of which is covered with a sheet of black paper to prevent thepermeation of light. The screenl0 is a 60 cross angle glass screenhaving a transparent-opaque ratio of 1:2 and a line pitch of 0.5 lm/mand the screen is placed 35 millimeters from the ground glass 24 of thecamera 23. The light source 9 may be a 100V, 500W projection lamp whichgives 90 seconds of exposure oflight to a lith type film 26 in a vacuumbag while the lens iris is set at f: 64. The film thereby exposed may bedeveloped using Kodaris Super developer with care not to causeirregularities in the development.

II. Photographing with printing frame. A. Equipment and material.

1. Printing frame. This may be an ordinary vacuum suction type printer.

2. Light source.

As a light source, there may be used a tungsten lamp which may belocated centrally at the bottom of the printing frame. Inserted betweenthe lamp and the top glass of the printer is an opal glass or suitablesynthetic resin, upon which is placed a photographically or mechanicallyfabricated grading mask having a greater transparency at the center andprogressively diminishing away from the center of the mask. In thismanner, theintensity of light is reduced progressively from the centertoward the periphery of the pattern. f

3. Screen.

A 60 cross angle screen or a white dot screen prepared therefrom withuse of a dry-plate or film which has a transparent portion of anysuitable configuration at each of an equilateral triangle may be used.

4. Photographic material.

A lith type or dry-plate may be used as in the-case of Process I above.

B. Process of preparing a pattern.

The apparatus required for the production of a master dot pattern inthis embodiment of the invention comprises a printing frame 27 having atop glass 28 upon which is placed a screen 29 with emulsified face upand a spacer of transparent sheet 30 placed on the screen.Alternatively, the screen 29 may be placed so that the emulsifiedsurface thereof firmly contacts the top glass 28 of the printing framethereby spacing the screen 29 uniformly from the emulsified face of thephotographic material 31 and thereby enabling the adjustment of screendot printing. The distance between the light source 32 and the printertop glass 28 is about 50 to 100 centimeters. A diffusing plate 33 madeof opal glass or synthetic resin is inserted in such a manner as topermit the distance (height) to be adjusted, and thus the grading ofscreen dots may be varied at will. Placed on the opal diffusing plate 33is a grading mask 35 which is covered at the periphery with a sheet ofblackpaper 34. The grading mask 35 may preferably be of disc form whichhas a diameter sufficiently large to cover the area required forexposure. The rest of the process involved in the printing of a masterdot pattern is the same as described in Process I hereinabove.

III. Photographing with graded-hole contact screen.

photographed. In this instance, the size of these ob scure screen dotsis reduced progressively from the center toward the peripheral portionof the screen by the effect of the grading mask. This-contact screen isadhered to a lith type film and exposed to light uniformly overv theentire surface, thereby obtaining a negative pattern having a clear-cutedge.

. The screen dot pa'ttern obtained from either of the aboveprocesses maybe provided with suitable symbols including a display line, a cuttingline, codes, numbers, etc., before it is finished asa photo-etchingmaster pattern.

Having thus described the principal concepts of the invention, it willbe obvious to those skilled in the art that various changes andmodifications may be made without limit to such specific embodiments asherein described and illustrated and without departing from the spiritand scope of the invention defined in the following claims. For example,the pore distribution may be concentrically elliptical instead ofconcentrically circular. Or, some pores may be larger or smaller thanthe others. 1

What is claimed is:

1. Apparatus for the production of a master dot pattern forphoto-etching of graded hole shadow masks in color television picturetubes comprising a light source, a photographic material spaced fromsaid light source and adapted to be formed as said master dot pattern, ascreen with a regular arrangement of openings therein positioned betweensaid light source and said photographic material, a grading maskadjacent said screen and between said source and photographic material,said grading mask comprising a flat plate of photographic materialhaving a progressively decreasing transparency from the center thereofto its periphery to control the exposure intensity in the central andperipheral portions of the master dot pattern without substantialdeflection of the light rays from said light source and a lens anddiaphragm between said mask and said'screen. v

2. Apparatus as claimed in claim 1 wherein said plate has a lighttransmittance characteristic arranged in concentric circular fashion,the transmittance decreasing from the center to the periphery.

SQApparatus as claimed in claim 2 wherein said plate comprises asuccession of stacked elements having uniform light transmittance andprovided with concentric openings which successively increase indiameter.

4. Apparatus as claimed in claim 2 wherein said plate is semitransparentand has uniform light transmittance, said plate having a conical recesstherein.

5. Apparatus as claimed in claim 1 comprising a circular disc having atransparent portion and an opaque portion, and comprising means toprovide relative rotation between said disc and said flat plate ofphotographic material, said transparent portion providing saidprogressively decreasing transparency.

' 6. Apparatus as claimed in claim 5 wherein said transparent portionhas one radial edge and one curved edge intersecting atthe center of thedisc, the curved edge being progressively further from the radial edgewith increasing radial distance. 1...; 7. Apparatus as claimed in claim5 wherein said transparent portion is an angular sector, and comprisingan optical wedge in said transparent portion with a density varyingradially in said wedge.

8. Apparatus as claimed in claim 1 comprising a printing frame, saidlight source being within said frame, a glass member on said frame, saidscreen being mounted on said glass member, said photographic materialhaving an emulsified surface and being mounted on said screen, said maskbeing in said frame between said source and said glass member.

9. Apparatus as claimed in claim 8 comprising a diffusing platesupporting said grading mask and adjustable in distance relative to saidsource and glass member.

1. Apparatus for the production of a master dot pattern forphoto-etching of graded hole shadow masks in color television picturetubes comprising a light source, a photographic material spaced fromsaid light source and adapted to be formed as said master dot pattern, ascreen with a regular arrangement of openings therein positioned betweensaid light source and said photographic material, a grading maskadjacent said screen and between said source and photographic material,said grading mask comprising a flat plate of photographic materialhaving a progressively decreasing transparency from the center thereofto its periphery to control the exposure intensity in the central andperipheral portions of the master dot pattern without substantialdeflection of the light rays from said light source and a lens anddiaphragm between said mask and said screen.
 2. Apparatus as claimed inclaim 1 wherein said plate has a light transmittance characteristicarranged in concentric circular fashion, the transmittance decreasingfrom the center to the periphery.
 3. Apparatus as claimed in claim 2wherein said plate comprises a succession of stacked elements havinguniform light transmittance and provided with concentric openings whichsuccessively increase in diameter.
 4. Apparatus as claimed in claim 2wherein said plate is semitransparent and has uniform lighttransmittance, said plate hAving a conical recess therein.
 5. Apparatusas claimed in claim 1 comprising a circular disc having a transparentportion and an opaque portion, and comprising means to provide relativerotation between said disc and said flat plate of photographic material,said transparent portion providing said progressively decreasingtransparency.
 6. Apparatus as claimed in claim 5 wherein saidtransparent portion has one radial edge and one curved edge intersectingat the center of the disc, the curved edge being progressively furtherfrom the radial edge with increasing radial distance.
 7. Apparatus asclaimed in claim 5 wherein said transparent portion is an angularsector, and comprising an optical wedge in said transparent portion witha density varying radially in said wedge.
 8. Apparatus as claimed inclaim 1 comprising a printing frame, said light source being within saidframe, a glass member on said frame, said screen being mounted on saidglass member, said photographic material having an emulsified surfaceand being mounted on said screen, said mask being in said frame betweensaid source and said glass member.
 9. Apparatus as claimed in claim 8comprising a diffusing plate supporting said grading mask and adjustablein distance relative to said source and glass member.